Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $23.96   6.682%   $25.561   $25.56   $25.55   $25.60  
  Purchase #2 $150.36   7.594%   $161.7783   $161.78   $161.80   $161.80  
  Purchase #3 $71.38   8.173%   $77.2139   $77.21   $77.20   $77.20  
  Purchase #4 $143.62   5.740%   $151.8638   $151.86   $151.85   $151.90  
  Purchase #5 $139.69   12.809%   $157.5829   $157.58   $157.60   $157.60  
  Purchase #6 $132.52   12.448%   $149.0161   $149.02   $149.00   $149.00  
  Purchase #7 $33.64   3.538%   $34.8302   $34.83   $34.85   $34.80  
  7 purchase totals = $695.17       $757.8462   $757.84   $757.85   $757.90